1. Field of the Invention
This invention relates to testing of telephone lines using time-domain reflectometry.
2. Description of the Prior Art
A typical telephone subscriber receives telephony services over a pair of copper wires at frequencies below 4 kHz. Recent transmission technology, such as digital subscriber line (DSL), has expanded the possible use of copper wires to enable high speed data transmissions using frequencies up to and beyond 1 MHz. However, installation practices and defects or anomalies in copper wire pairs can limit or distort the transmission carrying capacity thereof. To test for possible problems in copper wire pairs, a single-ended test is desired to avoid or minimize the time and expense of dispatching repair personnel to the far end of a copper wire pair for a dual-ended test.
Time-domain reflectometry (TDR) is a well-known and generally available technique that can be utilized to identify problems associated with copper wire pairs. TDR apparatus and methods are disclosed generally in U.S. Pat. Nos. 5,121,420 to Marr et al.; 5,369,366 to Piesinger; 5,461,318 to Borchertetal.; 5,521,512 to Hulina; 5,530,365 to Lefeldt; and 5,650,728 to Rhein et al.
Traditional TDR techniques, however, have several limitations. Specifically, present TDR techniques include transmitting an electrical pulse down the copper wire pair and measuring the time to receive a return pulse. This return pulse occurs when the transmitted pulse encounters a change in impedance of the copper wire pair due to some discontinuity therein. Common causes of discontinuities in the copper wire pair include: splices where different copper wire pairs are joined together; moisture on or around the copper wire pair; connection of bridged taps to the copper wire pair; or terminations, such as telephones, that may be connected to the copper wire pair.
Conventional TDR is limited by the energy content of the pulse and the frequency dispersion of the pulse as it travels along the length of the copper wire pair and back. These limitations include: technical difficulty in coupling all of the source TDR energy pulses to the copper wire pair; very low return signal levels due to losses associated with round trip pulse transmission along the copper wire pair; xe2x80x9csmearingxe2x80x9d of return pulses due to multiple reflections in both directions of pulse travel, and a low signal-to-noise ratio (SNR) on a lossy copper wire pair.
It is, therefore, an object of the present invention to provide an apparatus and method for detecting a loop configuration of a telephone line. This loop configuration can include: the length of the telephone line; the position of a bridged tap connected to the telephone line; and/or the length of the bridged tap connected to the telephone line. Still other objects of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description.
Accordingly, we have invented an apparatus for detecting discontinuities of a telephone line. The apparatus includes means for electrically stimulating a telephone line and a return detector for acquiring plural samples of data corresponding to the response of the telephone line to the electrical stimulation during at least one sample interval. A controller stores the plural samples of data and forms therefrom a plurality of windows of sampled data with each window including a unique subset of the plural samples of data. An activity finder receives each of the plurality of windows and outputs a weighting value for each window as a function of at least one of (i) the numerical values of the unique subset of the plural samples of data of the window; (ii) the relative position of the window in the plurality of windows; and (iii) the numerical range of values of the unique subsets of the plural samples of data forming the window. The controller can detect a predetermined event from a subset of the weighting values and can select one of the plurality of windows as a function of one of the weighting values of the subset of weighting values. An event identifier processes the one window and outputs to the controller as a function thereof a first value which is a numerical probability that the one window represents a discontinuity of the telephone line. The event identifier can also output as a function of the one window a second value which is a numerical probability that the one window represents an end-of-line (EOL) of the telephone line.
Preferably, the first value is a bridged tap (BT) value which relates to a position on the telephone line where a BT is connected. The first value can also relate to a position on the telephone line where a load coil is connected; a position on the telephone line where there is a change in the wire gauge of the wire forming the telephone line; and/or a position on the telephone line where there are faults or partially broken leads in the wire forming the telephone line. Preferably, the second value, also known as an EOL value, relates to the EOL of the telephone line. When the first value is a BT value, a BT length identifier processes the one window when the BT value is greater than the EOL value and outputs to the controller as a function of the BT value a BT length value. An EOL locator processes the one window and at least two of the BT value, the EOL value, the BT length value, the one weighting value of the subset of weighting values, the range of numerical values of the unique subset of the plural samples of data, and the relative location of the one window in the plurality of windows and outputs to the controller as a function thereof an EOL length value. When the BT value is greater than the EOL value, the relative position of the one window in the plurality of windows corresponds to a position on the telephone line where the BT is connected. When the EOL value is greater than the BT value, the relative position of the one window in the plurality of windows corresponds to a length of the telephone line.
The electrical stimulation can include a first pulse corresponding to a first section of the telephone line and a second pulse corresponding to a second section of the telephone line which is partially coincident with the first section of the telephone line. The response of the telephone line includes a first waveform corresponding to a response of the telephone line to the first pulse and a second waveform corresponding to a response of the telephone line to the second pulse. A part of the first waveform and a part of the second waveform represent the response of the telephone line where the first section of the telephone line is partially coincident with the second section of the telephone line.
A first subset of the plurality of windows can be associated with the part of the first waveform and a second subset of the plurality of windows can be associated with the part of the second waveform. The activity finder can determine for each window of the first subset of the plurality of windows a first weighting value associated with the first waveform and can determine for each window of the second subset of the plurality of windows a second weighting value associated with the second waveform. Each first weighting value forms with one of the second weighting values a pair of weighting values having their respective windows including samples of data related to the same section of the telephone line.
A BT counter can be included for receiving the weighting values of the plurality of windows and for forming from the received weighting values a first trace which includes weighting values associated with the first waveform and weighting values associated with the second waveform and which excludes for each pair of related first and second weighting values the minimum thereof. The BT counter also forms from the received weighting values a second trace which includes weighting values associated with the first waveform and weighting values associated with the second waveform and which excludes for each pair of related first and second weighting values the maximum thereof. The BT counter processes the first trace and the second trace to obtain a count of bridged taps connected to the telephone line.
This processing of the first trace and second trace by the BT counter can include determining for each of a plurality of predetermined threshold weighting values two or more of (i) a first value corresponding to an area of the first trace which is greater than the predetermined threshold weighting value; (ii) a second value corresponding to an area of the second trace which is greater than the predetermined threshold weighting value; (iii) a third value corresponding to a total area of the first trace which is associated with the area thereof which is greater than the predetermined threshold weighting value; and (iv) a fourth value corresponding to a total area of the second trace which is associated with the area thereof which is greater than the predetermined threshold weighting value. Processing of the first trace and the second trace can also include determining for each of a plurality of percentages at least one of (i) a first weighting value where a ratio of an area of the first trace above the first weighting value to the total area of the first trace equals the percentage and (ii) a second weighting value where a ratio of the area of the second trace above the second weighting value to the total area of the second trace equals the percentage. From two or more of the first through fourth values and at least one of the first and second weighting values at least one BT count value corresponding to the number of bridged taps connected to the telephone line can be determined.
The BT counter can also receive for each window the numerical range of values of the samples of data thereof, i.e., a difference between the largest numerical value of the window and the smallest numerical value of the window. Based on the temporal positions of the corresponding windows of sampled data, the BT counter arranges the largest range values into a third trace which excludes the smallest range value of each pair of ranges of values associated with the same section of telephone line and arranges the smallest range values into a fourth trace which excludes the largest range value of each pair of ranges of values associated with the same section of telephone line. For a plurality of predetermined threshold numerical values, the BT counter determines areas of the third trace and the fourth trace above each predetermined threshold numerical value. From the areas above each predetermined threshold numerical value, the BT counter determines at least one BT count value corresponding to the number of BTs connected to the telephone line.
The functions performed by one or more of the activity finder, the event finder, the BT length finder, the EOL finder and/or the BT counter can be implemented in one or more trained neural networks.
Preferably, the samples of data forming each window of sampled data are preferably decimated by N prior to the activity finder receiving each window. In one embodiment, N equals six (N=6).
The means for electrically stimulating the telephone line can include a charge generator for charging the telephone line to at least one predetermined voltage and a line clamp for connecting together two or more conductive wires which form the telephone line.
We have also invented an apparatus for detecting a discontinuity of a telephone line. The apparatus includes means for electrically stimulating a telephone line and a return detector for detecting during a sample interval a response waveform produced by the telephone line in response to the electrical stimulation. A controller stores the response waveform and forms therefrom a plurality of windows, with each window corresponding to a unique part of the response waveform. An activity finder determines a weighting value for each window as a function of at least two of (i) changes in the response waveform occurring in the window; (ii) the temporal position of the window in the plurality of windows; and (iii) the range of the response waveform in the window. The controller can detect a predetermined event in a subset of the weighting values and can select one of the plurality of windows as a function of one of the weighting values of the subset of weighting values. Preferably, the one window is selected based on its corresponding weighting value being the central weighting value in the subset of weighting values. An event identifier processes the one window to produce a first value which is a numerical probability that the one window represents a discontinuity of the telephone line. The event identifier can also output as a function of the one window a second value which is a numerical probability that the one window represents an EOL of the telephone line. Preferably, the first and second values are a BT value and an EOL value.
A BT length identifier processes the one window when the BT value is greater than the EOL value to produce a BT length value. An EOL locator determines an EOL length value as a function of at least two of the BT value, the EOL value, the BT length value, the one weighting value of the subset of weighting values, the range of the response waveform in the one window, and the relative position of the one window in the plurality of windows. When the BT value is greater than the EOL value, the BT length value corresponds to the length of a bridged tap connected to the telephone line and the temporal position of the one window in the plurality of windows corresponds to a position on the telephone line where the bridged tap is connected. When the EOL value is greater than the BT value, the temporal position of the one window in the plurality of windows corresponds to a length of the telephone line.
Lastly, we have invented a method of testing a telephone line. The method includes electrically stimulating a telephone line and detecting during a sample interval a response waveform produced by the telephone line in response to the electrical stimulation. The response waveform is stored and a plurality of windows is formed therefrom, with each window corresponding to a unique part of the response waveform. A weighting value is determined for each window as a function of at least two of (i) changes in the response waveform occurring in the window; (ii) the temporal location of the window in the sample interval; and (iii) the range of the response waveform in the window. A predetermined event is detected in a subset of the weighting values and one of the plurality of windows is selected as a function of one of the weighting values of the subset of weighting values. The one window is processed to produce a first value which is a numerical probability that the one window represents a discontinuity of the telephone line. The one window can also be processed to produce at least one of a second value and a third value, where the second value is a numerical probability that the one window represents an EOL of the telephone line. Preferably, the first, second and third values are a BT value, an EOL value and a BT length value, respectively.
An EOL length value can be determined as a function of at least two of the BT value; the EOL value; the BT length value; the one weighting value of the subset of weighting values; the range of the response waveform in the one window; and the temporal location of the one window in the sample interval. When the BT value is greater than the EOL value, the BT length value corresponds to the length of a bridged tap connected to the telephone line and the temporal location of the one window in the sample interval corresponds to the position of the bridged tap on the telephone line. When the EOL value is greater than the BT value, the temporal location of the one window in the sample interval corresponds to a length of the telephone line.
The response waveform can include a first waveform corresponding to a response of the first part of the telephone line and a second waveform corresponding to a response of a second part of the telephone line. A part of the first waveform and a part of the second waveform correspond to the response of the telephone line where the first part of the telephone line is partially coincident with the second part of the telephone line.
The part of the first waveform and the part of the second waveform each have one or more windows associated therewith. Each window of the part of the first waveform is related to one window of the part of the second waveform based upon their respective waveforms being related to a common section of the telephone line.
For each window of the first waveform, a first weighting value is determined and for each window of the second waveform a second weighting value is determined. The weighting values are utilized to form a first trace which includes weighting values related to the first waveform and weighting values related to the second waveform, which excludes for each related pair of first and second weighting values the minimum thereof. Also formed from the weighting values is a second trace which includes weighting values related to the first waveform and weighting values related to the second waveform, which excludes for each related pair of first and second weighting values the maximum thereof. The first trace and the second trace can be processed to obtain a count of bridged taps connected to the telephone line.
The numerical range of the samples of data forming the response waveform in each window can be determined and, based on the temporal positions of each window of the plurality of windows, the maximum range values can be arranged into a third trace which excludes the minimum range value of each pair of ranges of values associated with the same section of the telephone line, and the minimum range values can be arranged into a fourth trace which excludes the maximum range of each pair of ranges of values associated with the same section of the telephone line. A plurality of predetermined threshold numerical values can be provided and areas of the third trace and the fourth trace can be determined above each predetermined threshold numerical value. As a function of the areas of the third and fourth traces above each of the predetermined numerical threshold values, the number of BTs connected to the telephone line can be determined.